The colour of fabrics can be altered during the laundering process or during wear or use by photo fading.
The fading of coloured fabrics by sunlight during wear, and during drying, is a major problem for consumers. Sun fading of fabrics is of specific concern to consumers because the contrast between exposed and unexposed areas makes it particularly noticeable. e.g. on collars, inside versus outside of garments, and on wrap around garments such as saris.
In addition, and especially important because of health considerations, consumers rely on the use of clothes to protect them from UV light. However, as the light weight clothing worn in hot countries provides little protection from UV light it is frequently and increasingly beneficial to enhance the UV protection given by clothes. These effects can be mitigated by treating the fabrics with a sunscreen, usually applied as one component of a detergent composition used to wash the fabrics. Sunscreens absorb UV radiation. Other materials which absorb UV radiation are fluorescers (sometimes called optical brighteners) which re-emit the absorbed radiation in the visible spectrum. For this reason, many sunscreens are also fluorescers, although it is possible for sunscreens to re-emit outside the visible range.
For example, U.S. Pat. No. 4,788,054 teaches the use of N-phenylphthalisomides as ultraviolet radiation absorbers for cotton, wool, polyester and rayon. Fabric care compositions comprising a water dispersible/water soluble copolymers which prevent photofading are disclosed in EP-A-0 523 956.
WO-A-96/03369 discloses the use of butylated hydroxy toluene for the protection of surfaces from physical and chemical degradation.
Recently, it has been reported (Skin Protection against Ultraviolet Light by Cotton Textiles treated with Optical Brighteners, D. Reiner et al, in Proceedings of the 4th World Surfactants Congress (CESIO, Barcelona, 1996) Vol 1, pp. 264-276) that there is an increasing requirement for skin protection against both UV-A and UV-B sunlight. It was reported that certain optical brighteners were especially suited to endowing garments with sunlight protection capability. On the basis of this observation, new compounds were developed especially for that purpose. These are described and claimed in EP-A-0 728 749 which discloses the preparation and use of sunscreen of the formula (I) as hereinafter defined, in liquid detergent compositions comprising more than 5% by weight of builder salts.
There is, however, a persistent problem that in liquid detergent compositions it is difficult to formulate a composition that mitigates photofading and increases the UV barrier of fabrics, whilst remaining of a transparent appearance (in the absence of opacifier). Sunscreens of general formula (I) are known to produce a hazy or cloudy composition when included in conventional transparent liquid detergent compositions. It has proved difficult to incorporate compounds such as disclosed in EP-A-0 728 749 in a stable fashion in aqueous liquid detergent compositions, particularly those of the isotropic kind, and especially, those containing polymers for soil release or anti-dye transfer, or containing enzyme stabilising systems that contribute to soil removal, without inducing formation of structured phases which cause the composition to become opaque and ultimately, lead to physical instability.
In a first aspect, the present invention provides the solution of formulating liquid detergent compositions in substantially transparent form by incorporating less than 5% by weight of builder salts, based on the weight of the total composition.
In a second aspect, the present invention provides the solution of formulating the liquid detergent compositions in substantially clear form by incorporating a water-miscible polar organic solvent.
In the context of the second aspect of the present invention, it should be noted that European patent application WO 92/06172 discloses formulation of a highly built aqueous liquid detergent containing an optical brightener and a polyhydroxy fatty acid amide, wherein the brightener is added to the detergent composition in admixture with the polyhydroxy fatty acid amide. The compositions disclosed contain mixtures of builders selected from a very wide range, present in at least 10% by weight, usually much more.